The James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) was one of the first legacy surveys with the JCMT in Hawaii, mapping 47 deg2 of nearby (<500 pc) molecular clouds in dust continuum ...emission at 850 and 450 m, as well as a more limited area in lines of various CO isotopologues. While molecular clouds and the material that forms stars have structures on many size scales, their larger-scale structures are difficult to observe reliably in the submillimeter regime using ground-based facilities. In this paper, we quantify the extent to which three subsequent data reduction methods employed by the JCMT GBS accurately recover emission structures of various size scales, in particular, dense cores, which are the focus of many GBS science goals. With our current best data reduction procedure, we expect to recover 100% of structures with Gaussian sizes of ≤30″ and intensity peaks of at least five times the local noise for isolated peaks of emission. The measured sizes and peak fluxes of these compact structures are reliable (within 15% of the input values), but source recovery and reliability both decrease significantly for larger emission structures and fainter peaks. Additional factors such as source crowding have not been tested in our analysis. The most recent JCMT GBS data release includes pointing corrections, and we demonstrate that these tend to decrease the sizes and increase the peak intensities of compact sources in our data set, mostly at a low level (several percent), but occasionally with notable improvement.
We present Herschel far-infrared and submillimeter maps of the debris disk associated with the HR 8799 planetary system. We resolve the outer disk emission at 70, 100, 160, and 250 mu m and detect ...the disk at 350 and 500 mu m. A smooth model explains the observed disk emission well. We observe no obvious clumps or asymmetries associated with the trapping of planetesimals that is a potential consequence of planetary migration in the system. We estimate that the disk eccentricity must be <0.1. As in previous work by Su et al., we find a disk with three components: a warm inner component and two outer components, a planetesimal belt extending from 100 to 310 AU, with some flexibility (+ or - 10 AU) on the inner edge, and the external halo that extends to ~2000 AU. We measure the disk inclination to be 26degrees + or - 3degrees from face-on at a position angle of 64degrees E of N, establishing that the disk is coplanar with the star and planets. The spectral energy distribution of the disk is well fit by blackbody grains whose semi-major axes lie within the planetesimal belt, suggesting an absence of small grains. The wavelength at which the spectrum steepens from blackbody, 47 + or - 30 mu m, however, is short compared with other A star debris disks, suggesting that there are a typically small grains likely populating the halo. The PACS longer wavelength data yield a lower disk color temperature than do MIPS data (24 and 70 mu m), implying two distinct halo dust-grain populations.
YOUNG STELLAR OBJECTS IN THE GOULD BELT Dunham, Michael M.; Allen, Lori E.; Evans II, Neal J. ...
The Astrophysical journal. Supplement series,
09/2015, Volume:
220, Issue:
1
Journal Article
Peer reviewed
Open access
ABSTRACT We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks" (c2d) and "Gould Belt" (GB) Legacy ...surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the GB. We compile extinction corrected spectral energy distributions for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0 + I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background Asymptotic Giant Branch stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0 + I YSOs and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0 + I sample is classified as Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr (Class I). We revisit infrared color-color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.
Motivated by the long-standing "luminosity problem" in low-mass star formation whereby protostars are underluminous compared to theoretical expectations, we identify 230 protostars in 18 molecular ...clouds observed by two Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We compile complete spectral energy distributions, calculate L sub(bol) for each source, and study the protostellar luminosity distribution. This distribution extends over three orders of magnitude, from 0.01 L sub(odot) to 69 L sub(odot), and has a mean and median of 4.3 L sub(odot) and 1.3 L sub(odot), respectively. The distributions are very similar for Class 0 and Class I sources except for an excess of low luminosity (L sub(bol) lap 0.5 L sub(odot)) Class I sources compared to Class 0. 100 out of the 230 protostars (43%) lack any available data in the far-infrared and submillimeter (70 mu m < lambda < 850 jim) and have L sub(bol) underestimated by factors of 2.5 on average, and up to factors of 8-10 in extreme cases. Correcting these underestimates for each source individually once additional data becomes available will likely increase both the mean and median of the sample by 35% h-bar 0%. We discuss and compare our results to several recent theoretical studies of protostellar luminosities and show that our new results do not invalidate the conclusions of any of these studies. As these studies demonstrate that there is more than one plausible accretion scenario that can match observations, future attention is clearly needed. The better statistics provided by our increased data set should aid such future work.
THE DISK AROUND THE BROWN DWARF KPNO TAU 3 Broekhoven-Fiene, Hannah; Matthews, Brenda; Duchene, Gaspard ...
The Astrophysical journal,
07/2014, Volume:
789, Issue:
2
Journal Article
Peer reviewed
Open access
We present submillimeter observations of the young brown dwarfs KPNO Tau 1, KPNO Tau 3, and KPNO Tau 6 at 450 mum and 850 mum taken with the Submillimetre Common-User Bolometer Array on the James ...Clerk Maxwell Telescope. KPNO Tau 3 and KPNO Tau 6 have been previously identified as Class II objects hosting accretion disks, whereas KPNO Tau 1 has been identified as a Class III object and shows no evidence of circumsubstellar material. Our 3sigma detection of cold dust around KPNO Tau 3 implies a total disk mass of (4.0 + or - 1.1) x 10 super(-4) M sub(middot in circle) (assuming a gas to dust ratio of 100:1). We place tight constraints on any disks around KPNO Tau 1 or KPNO Tau 6 of <2.1 x 10 super(-4) M sub(middot in circle) and <2.7 x 10 super(-4) M sub(middot in circle), respectively. Modeling the spectral energy distribution of KPNO Tau 3 and its disk suggests the disk properties (geometry, dust mass, and grain size distribution) are consistent with observations of other brown dwarf disks and low-mass T-Tauri stars. In particular, the disk-to-host mass ratio for KPNO Tau 3 is congruent with the scenario that at least some brown dwarfs form via the same mechanism as low-mass stars.
We present observations of the Auriga-CaliforniaMolecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 mum observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy ...Survey. The total mapped areas are 2.5 deg super(2) with IRAC and 10.47 deg super(2) with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHalpha 101 cluster and the filament extending from it.We present a quantitative description of the degree of clustering and discuss the relative fraction of YSOs in earlier (Class I and F) and later (Class II) classes compared to other clouds.We perform simple SED modeling of the YSOs with disks to compare the mid-IR properties to disks in other clouds and identify 14 classical transition disk candidates. Although the AMC is similar in mass, size, and distance to the OMC, it is forming about 15-20 times fewer stars.
We present observations of the debris disk around gamma Doradus, an F1V star, from the Herschel Key Programme DEBRIS (Disc Emission via Bias-free Reconnaissance in the Infrared/Submillimetre). The ...disk is well resolved at 70, 100, and 160 mum, resolved along its major axis at 250 mum, detected but not resolved at 350 mum, and confused with a background source at 500 mum. It is one of our best resolved targets and we find it to have a radially broad dust distribution. The modeling of the resolved images cannot distinguish between two configurations: an arrangement of a warm inner ring at several AU (best fit 4 AU) and a cool outer belt extending from ~55 to 400 AU or an arrangement of two cool, narrow rings at ~70 AU and ~190 AU. This suggests that any configuration between these two is also possible. Both models have a total fractional luminosity of ~10 super(-5) and are consistent with the disk being aligned with the stellar equator. The inner edge of either possible configuration suggests that the most likely region to find planets in this system would be within ~55 AU of the star. A transient event is not needed to explain the warm dust's fractional luminosity.
The Auriga-California Molecular Cloud (AMC) is one of two nearby (within 500 pc) giant molecular clouds, the other being the Orion A Molecular Cloud (OMC). We aim to study the properties of ...circumstellar disks in the AMC to compare the planet formation potential and processes within the AMC to those for other clouds. A first look with measurements from Spitzer observations suggests that AMC disk properties, such as the distribution of disk luminosities and the evolution of the mid-IR excesses, are not vastly different from those in other regions. Follow-up observations in the submm, mm and cm can be used to measure disk masses and the degree of grain growth from spectral slopes to more completely characterize the disk population.
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